Solid‐Liquid and Liquid‐Vapor Phase Transitions: Similarities and Differences

Abstract

Every theory, whether in the physical or biological or social sciences, distorts reality in that it oversimplifies. But if it is a good theory, what is omitted is outweighted by the beam of light and understanding thrown over diverse facts. Paul A. SamuelsonA comparison has been made between the behavior of the thermodynamic properties of simple substances along the curves of solid-liquid and liquid-vapor phase equilibrium. Hereby the attention is concentrated on the internal pressure p i , the isothermal elasticity −(∂ p/∂v) T , the surface energy of the interfacial boundary σ , and the viscosity of the liquid, η. The mentioned curves have been extended beyond the triple point into the region of coexistence of metastable phases. Both phase transitions considered approach here the boundaries of stability of the liquid, but in opposite directions from the triple point with respect to variations of temperature and pressure. Among other consequences, the difference in the thermodynamic behavior of one-component systems for both types of phase transformations, as established in the analysis, gives support to the theoretical idea of the absence of a critical point for the solid-liquid phase equilibrium curve.where s SL = s L − s S , v SL = v L − v S are entropy and volume changes during melting, respectively. But there are also significant qualitative distinctions between the behavior of the liquidvapor and solid-liquid equilibrium coexistence curves. One of them consists in the fact that the phase coexistence curve for liquid-vapor equilibrium p = p LV (T ) has a lower limit at pressure p = 0, whereas the solid-liquid coexistence curve may be extended into the region Nucleation Theory and Applications. edited by J. W. P. Schmelzer